In known dispensing devices for milk and/or milk foam, usually milk is mixed with steam (in particular water vapor) and possibly air, to produce heated milk or milk foam and/or a mixture of heated milk and milk foam. Such dispensing devices are frequently also integrated in coffee machines, particularly as coffee machines generally also comprise a device for producing water vapor. Coffee machines comprising an integrated dispensing device for milk and/or milk foam in the known manner make it possible to produce either coffee (without the addition of milk) or heated milk (without the addition of coffee) or white coffee (without the addition of milk foam) or speciality coffees, which contain milk foam or foamed milk (for example cappuccino or latte macchiato).
In dispensing devices for milk and/or milk foam, which are used in combination with coffee machines, generally a vacuum is produced (“Venturi effect”) by a jet of steam in a suitably shaped nozzle (“Venturi nozzle”) which makes it possible to suck from a reservoir (milk container) filled with milk a portion of milk via a line between the nozzle and the reservoir and to conduct said portion of milk into the nozzle. To produce heated milk only (without milk foam), the suctioned milk may be mixed in a chamber of the respective dispensing device with the steam injected into the nozzle and, as a result, heated. Subsequently, the milk-steam-mixture thus produced may be dispensed in the form of a steady output jet from the dispensing device via an outlet into a suitable receptacle. To produce milk foam and/or foamed milk, additional air may be suctioned with the steam jet (for example via a continuous line for the ambient air) and mixed in the chamber with the respective suctioned milk. In this variant, a milk-steam-air mixture in the form of a steady output jet may be dispensed from the chamber via the outlet into a suitable receptacle, in this case a mixture of heated milk and milk foam being collected in the receptacle.
Hitherto, a plurality of dispensing devices for milk and/or milk foam of the aforementioned type, based on a mixture of milk, steam and air have been proposed, which permit a user to produce milk and/or milk foam in different variants.
For example, a dispensing device for producing milk foam is known from EP 1 115 317 B1, in which a flow of the milk respectively suctioned by a steam jet with a valve which is arranged in a line for supplying milk and which comprises a manually adjustable regulating shaft for regulating a supply of milk, may be preselected by a manual adjustment of the regulating shaft and/or altered by a manual adjustment of the regulating shaft. The regulating shaft is an adjustable body with a through-hole for the milk. By a suitable adjustment of the regulating shaft a user may influence and/or limit the quantity of milk suctioned by means of a steam jet. The air respectively suctioned and mixed with the milk may not be specifically influenced in this dispensing device. This dispensing device has the drawback that the possibility of producing different types of milk and/or milk foam is limited. As only the quantity of suctioned milk may be altered by adjusting the regulating shaft, a user is only able to foam milk with this dispensing device and thus at best influence the quantity and the temperature of the milk foam produced and/or the mixture of heated milk and milk foam produced. A use of this dispensing device in combination with a coffee machine is, therefore, extremely awkward for a user with regard to the production of speciality coffees, which are based on a combination of coffee, milk and/or milk foam, particularly because before producing a specific coffee speciality the user firstly has to determine by experimentation the optimal setting of the regulating shaft of the valve which corresponds to the wishes of the user. Several attempts at this are generally necessary. In this connection, it is a drawback that a manual adjustment of the regulating shaft is generally time-consuming and only able to be duplicated inaccurately. It is, therefore, difficult for a user to produce different types of milk foam and/or a mixture of heated milk and milk foam and/or different types of speciality coffees.
A dispensing device based on a mixture of milk, steam and air for producing milk foam and heated milk is also known from EP 1 688 074 B1, in which an inlet opening for air in a line for supplying air comprising a valve for controlling the air supply may be selectively opened or closed. A closure body of the valve may be moved by means of an electric motor to selectively open the valve by activating the electric motor and in this manner to permit the supply of air or to close the valve and in this manner to prevent the supply of air. The dispensing device further comprises a line for the supply of milk, a user having no possibility of regulating (i.e. switching off, switching on and/or varying) a flow of milk through this line. In this dispensing device, therefore, a user may suck a predetermined quantity of milk with a steam jet and at the same time mix the suctioned air either with the steam and a predetermined quantity of air (provided the valve is opened for controlling the air supply) or simply mix with the steam (provided the valve is closed for controlling the air supply). In this dispensing device, by actuating the valve a user only has the possibility of producing two different types of milk beverages: a predetermined quantity of heated milk without a proportion of milk foam (with the valve closed) or a predetermined quantity of foamed milk with a predetermined consistency (with the valve open). This dispensing device also has the drawback, therefore, that the possibility of producing different types of milk and/or milk foam is limited. In combination with a coffee machine, therefore, this dispensing device also provides a user with little freedom of choice when producing speciality coffees, which are based on a combination of coffee, milk and/or milk foam.